swell

Though many ﬁrst picture a swell as a feature of the ocean’s surface, the term is also used to identify a long, roundly arched, often isolated elevation on the surface of the Earth, created where soil absorbs a great deal of water. Used in this way, the term usually includes an adjective, such as broad, bulging, undulating, protruding, round, or oval. Isolated swells are sometimes called domes or arches, though these terms are technically inaccurate. Swells are correctly called rises when found on extensive plains in combination with the depressions known as swales, the rises being part of an undulating, wet-and-dry, swale-and-rise topography, formed by the differential melting of glacial ice, which once stretched for hundreds of miles across the Midwest. Perhaps the best-known swell in North America is the domal San Rafael Swell in southeastern Utah. From the air, its eastern front resembles a ﬁfty-milelong wave advancing across the desert, even to its seeming to break in a sea of froth over a spectacular “reef” of white Navajo Sandstone along its eastern perimeter. Formed forty to sixty million years ago, this twothousand-foot-high swell bowed up so slowly that three rivers in the area—the San Rafael, the Muddy, and the Price—were able to maintain their courses across the uplifted land. They continue to cross the swell today.